The present invention relates to novel compounds, pharmaceutical compositions thereof and methods of using them in the treatment of stroke, cerebral ischemia, pain, epilepsy, and head trauma. In particular, the present invention relates to reduced backbone dipeptide compounds that are potent antagonists of N-type calcium channels.
The entry of excessive amounts of calcium ions into neurons following an ischemic episode or other neuronal trauma has been well documented. Uncontrolled high concentrations of calcium in neurons initiate a cascade of biochemical events that disrupts normal cellular processes. Among these events are the activation of proteases and lipases, breakdown of neuronal membranes, and the formation of free radicals, which may ultimately lead to cell death. Several types of calcium channels have been discovered: the L, N, P, Q, R,,and T types. Each type possesses distinct structural features, functional properties, and cellular/subcellular distributions. N-type calcium channels are tissue specific, restricted to the central and peripheral neurons of the forebrain and areas rich in synaptic connections. They have well defined roles, e.g., regulation of calcium flux necessary for depolarization-evoked release of transmitter from synaptic endings; and they can be selectively blocked by high-affinity ligands, like xcexa9-conotoxins and synthetic analogs. Bowersox S. S., et al., Drug News and Perspective, 1994;7:261-268.
The present invention provides novel compounds and compositions that are capable of blocking N-type calcium channels. The compounds are useful in a method for treating afflictions associated with increased calcium ion uptake through N-type calcium channels, including such systemic effects as stroke, cerebral ischemia resulting from cardiac arrest, head trauma, closed head injury, pain, and epilepsy. Further advantages of this invention will be clear to one skilled in the art from the reading of the description that follows.
The present invention comprises new compounds and, more particularly, novel reduced backbone dipeptide compounds that are useful as N-type calcium channel blockers in mammals. The novel compounds of the present invention are represented by the following structural Formula I: 
wherein A, B, X, R1, R2, R3, and R6 are defined in more detail below and generally form a reduced dipeptide backbone.
The invention also includes novel compositions of matter containing the above-defined compound that are useful as neuroprotective agents for the treatment of afflictions associated with increased calcium ion uptake through N-type calcium channels in mammals, as well as the methods of treatment using such compositions.
The foregoing merely summarizes certain aspects of the present invention and is not intended, nor should it be construed, as limiting the invention in any manner. All patents and other publications referenced herein are hereby incorporated by reference in their entirety.
The present invention comprises novel reduced backbone dipeptide compounds and pharmaceutical compositions thereof that are useful as N-type calcium channel antagonists.
The novel compounds of the present invention have the following generic structural Formula I: 
wherein
R1 is H or methyl,
R2 is H, azepanylcarbonyl, C1-C7 alkyl, xe2x80x94(CH2)n-phenyl, wherein the phenyl is unsubstituted or substituted with C1-C4 alkyl, C1-C4 alkoxy, or halo,
R3 is C1-C5 alkyl,
X is xe2x80x94NR4R5 or xe2x80x94OR7,
R4 and R5 are independently H, C1-C5 alkyl, or
R4 and R5 together with the nitrogen to which they are both bound form: 
R6 is xe2x80x94(CH2)n-phenyl, wherein the phenyl is unsubstituted or substituted with C1-C4 alkyl, C1-C4 alkoxy, or halo,
A and B are independently xe2x80x94COxe2x80x94 or xe2x80x94CH2xe2x80x94, provided that A and B are not both xe2x80x94COxe2x80x94,
R7 is C1-C5 alkyl,
Z is xe2x80x94CH2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, or xe2x80x94N(R8)xe2x80x94,
R8 is H or C1-C6 alkyl, and n is 1 or 2.
In a preferred embodiment of the compound of Formula I, R4 and R5 are independently H, C1-C5-alkyl, or R4 and R5 taken together with the nitrogen to which they are both bound form 1-pyrrolidinyl, 1-piperidinyl, or 1-azepanyl, or R4 and R5 taken together with the nitrogen to which they are both bound are: 
and Z is xe2x80x94Sxe2x80x94 or xe2x80x94Oxe2x80x94.
Also provided are pharmaceutically acceptable salts, esters, amides, and pro-drugs of the compounds of the Formula I.
The term xe2x80x9calkylxe2x80x9d means a straight or branched chain hydrocarbon. Representative examples of alkyl groups are methyl, ethyl, propyl, isopropyl, isobutyl, butyl, tert-butyl, sec-butyl, pentyl, hexyl, (CH3)2CHCH2CH2xe2x80x94, (CH3)3CCH2CH2xe2x80x94, and heptyl.
The term xe2x80x9calkoxyxe2x80x9d means an alkyl group attached to an oxygen atom. Representative examples of alkoxy groups include methoxy, ethoxy, tert-butoxy, propoxy, and isobutoxy.
In a preferred embodiment, compounds of the invention are selected from the group consisting of:
2-((2-(Azaperhydroepinylcarbonylamino)-4-methylpentyl)amino)-N-(tert-butyl)-3-(4-(phenylmethoxy)phenyl)-(2S)-propanamide;
[S-(R*,R*)]-Azepane-1-carboxylic acid {1-[2-(4-benzyloxy-phenyl)-1-tert-butoxymethyl-ethylcarbamoyl]-3-methyl-butyl}-amide;
[S-(R*,R*)]Azepane-1-carboxylic acid (1-{[2-(4-benzyloxy-phenyl)-1-tert-butylcarbamoyl-ethylamino]-methyl}-3-methyl-butyl)-amide;
[S-(R*,R*)]-2-Dimethylamino-4-methyl-pentanoic acid [2-(4-benzyloxy-phenyl)-1-morpholin-4-ylmethyl-ethyl]-amide;
[S-(R*,R*)]-Azepane-1-carboxylic acid {1-[2-(4-benzyloxy-phenyl)-1-morpholin-4-ylmethyl-ethylcarbamoyl]-3-methyl-butyl}-amide;
[S-(R*,R*)]Azepane-1-carboxylic acid {1-[2-(4-benzyloxy-phenyl)-1-(tert-butylamino-methyl)-ethylcarbamoyl]-3-methyl-butyl}-amide;
(S,S)-Azepane-1-carboxylic acid {1-[2-(4-benzyloxy-phenyl)-1-diethylaminomethyl-ethylcarbamoyl]-3-methyl-butyl}-amide;
(S)-2-(2-Amino-4-methyl-pentylamino)-3-(4-benzyloxy-phenyl)-N-tert-butyl-propionamide dihydrochloride; and
2-(2-Amino-4-methyl-pentylamino)-3-(4-benzyloxy-phenyl)-N-tert-butyl-propionamide dihydrochloride.
The compounds of the invention may be readily prepared as set forth in the following reaction scheme(s) which employ general synthetic methods well-known to those skilled in organic chemistry. The following definitions apply:

wherein Ra-Rg are any chemical moiety consistent with the definitions of R1-R7.
The compounds of the invention are also useful research tools for studying the biological, cellular effects of blocking N-type calcium channels.
The invention further comprises a pharmaceutical composition for the treatment of illnesses induced by uncontrolled high concentrations of calcium in neurons, which composition comprises a compound of Formula I as defined above or, a pharmaceutically acceptable salt, solvent or pro-drug thereof, in an amount effective in the treatment of said illnesses, and a pharmaceutically acceptable carrier. The invention also comprises a pharmaceutical composition for the treatment of afflictions associated with increased calcium ion uptake through N-type calcium channels, including such systemic effects as stroke, pain, cerebral ischemia, head trauma, and epilepsy, which comprises a compound of Formula I as defined above in an amount effective in the treatment of said disorders, and a pharmaceutically acceptable carrier. Preferred compositions of the invention are those containing preferred compounds of Formula I as described above. The compounds will be administered to mammals at the rate of about 0.01 to about 200 mg/kg. Typical daily doses will be about 5 to about 500 mg per patient.
The term xe2x80x9cpro-drugxe2x80x9d refers to compounds that are rapidly transformed in vivo to yield the parent compound of the above formulae, for example, by hydrolysis in blood. A thorough discussion is provided in T. Higuchi and V. Stella, xe2x80x9cPro-drugs as Novel Delivery Systems,xe2x80x9d Vol 14 of the A.C.S. Symposium Series, and in Bioreversible Carriers in Drug Design, ed. Edward B. Roche, American Pharmaceutical Association and Pergamon Press, 1987, both of which are incorporated herein by reference.
The invention further relates to a method for the treatment of illnesses induced by uncontrolled high concentrations of calcium in neurons by administering to a subject in need of such treatment a compound of Formula I as defined above in an amount effective in such treatment, and a method for the treatment of stroke, pain, cerebral ischemia, head trauma, and epilepsy utilizing a compound of Formula I as defined above in an amount effective in such treatment. Preferred methods of the invention are those administering a preferred compound of the Formula I as described above.
The compounds of the present invention may be administered to a patient either alone or as part of a pharmaceutical composition. The compositions may be administered to patients either orally, rectally, parenterally (intravenously, intramuscularly, or subcutaneously), intracisternally, intravaginally, intraperitoneally, intravesically, locally (powders, ointments, or drops), or as a buccal or nasal spray.
Compositions suitable for parenteral injection may comprise physiologically acceptable sterile aqueous or non-aqueous solutions, dispersions, suspensions or emulsions, and sterile powders for reconstitution into sterile injectable solutions or dispersions. Examples of suitable aqueous and non-aqueous carriers, diluents, solvents or vehicles include water, ethanol, polyols (propyleneglycol, polyethyleneglycol, glycerol, and the like), suitable mixtures thereof, vegetable oils (such as olive oil), and injectable organic esters such as ethyl oleate. Proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersions, and by the use of surfactants.
These compositions may also contain adjuvants such as preserving, wetting, emulsifying, and dispensing agents. Prevention of the action of microorganisms can be ensured by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, and the like. It may also be desirable to include isotonic agents, for example sugars, sodium chloride, and the like. Prolonged absorption of the injectable pharmaceutical form can be brought about by the use of agents delaying absorption, for example, aluminum monostearate and gelatin.
Solid dosage forms for oral administration include capsules, tablets, pills, powders, and granules. In such solid dosage forms, the active compound is admixed with at least one inert customary excipient (or carrier) such as sodium citrate or dicalcium phosphate or (a) fillers or extenders, as for example, starches, lactose, sucrose, glucose, mannitol, and silicic acid, (b) binders, as for example, carboxymethylcellulose, alignates, gelatin, polyvinylpyrrolidone, sucrose, and acacia, (c) humectants, as for example, glycerol, (d) disintegrating agents, as for example, agar-agar, calcium carbonate, potato or tapioca starch, alginic acid, certain complex silicates, and sodium carbonate, (e) solution retarders, as for example, paraffin, (f) absorption accelerators, as for example, quaternary ammonium compounds, (g) wetting agents, as for example, cetyl alcohol, and glycerol monostearate, (h) adsorbents, as for example, kaolin bentonite, and (i) lubricants, as for example, talc, calcium stearate, magnesium stearate, solid polyethylene glycols, sodium lauryl sulfate, or mixtures thereof. In case of capsules, tablets, and pills, the dosage forms may also comprise buffering agents.
Solid compositions of a similar type may also be employed as fillers in soft and hard-filled gelatin capsules using such excipients as lactose or milk sugar as well as high molecular weight polyethyleneglycols, and the like.
Solid dosage forms such as tablets, dragees, capsules, pills, and granules can be prepared with coatings and shells, such as enteric coatings and others well known in the art. They may contain opacifying agents, and can also be of such composition that they release the active compound or compounds in a certain part of the intestinal tract in a delayed manner. Examples of embedding compositions that can be used are polymeric substances and waxes. The active compounds can also be in micro-encapsulated form, if appropriate, with one or more of the above-mentioned excipients.
Liquid dosage forms for oral administration include pharmaceutically acceptable emulsions, solutions, suspensions, syrups, and elixirs. In addition to the active compounds, the liquid dosage forms may contain inert diluents commonly used in the art, such as water or other solvents, solubilizing agents and emulsifiers, as for example, ethyl alcohol, isopropyl alcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzyl benzoate, propyleneglycol, 1,3-butyleneglycol, dimethylformamide, oils (in particular, cottonseed oil, groundnut oil, corn germ oil, olive oil, castor oil, and sesame oil), glycerol, tetrahydrofurfuryl alcohol, polyethyleneglycols and fatty acid esters of sorbitan or mixtures of these substances, and the like.
Besides such inert diluents, the composition can also include adjuvants such as wetting agents, emulsifying and suspending agents, sweetening agents, flavoring agents, and perfuming agents.
Suspensions, in addition to the active compounds, may contain suspending agents, as for example, ethoxylated isostearyl alcohols, polyoxyethylene sorbitol and sorbitan esters, microcrystalline cellulose, aluminum metahydroxide, bentonite, agar-agar, and tragacanth, or mixtures of these substances, and the like.
Compositions for rectal or intravaginal administrations are preferably suppositories which can be prepared by mixing the compounds of the present invention with suitable non-irritating excipients or carriers such as cocoa butter, polyethyleneglycol, or a suppository wax, which are solid at ordinary temperatures but liquid at body temperature and therefore, melt in the rectum or vaginal cavity and release the active compound.
Dosage forms for topical administration of a compound of this invention include ointments, powders, sprays, and inhalants. The active component is admixed under sterile conditions with physiologically acceptable carrier and any preservatives, buffers, or propellants as may be required. Ophthalmic formulations, eye ointments, powders, and solutions are also contemplated as being within the scope of this invention.
The term xe2x80x9cpharmaceutically acceptable salts, esters, amides, and pro-drugsxe2x80x9d as used herein refers to those carboxylate salts, amino acid addition salts, esters, amides, and pro-drugs of the compounds of the present invention which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of patients without undue toxicity, irritation, allergic response, and the like, commensurate with a reasonable benefit/risk ratio, and effective for their intended use, as well as the zwitterionic forms, where possible, of the compounds of the invention. The term xe2x80x9csaltsxe2x80x9d refers to the relatively non-toxic, inorganic and organic acid addition salts of compounds of the present invention. These salts can be prepared in situ during the final isolation and purification of the compounds or by separately reacting the purified compound in its free base form with a suitable organic or inorganic acid and isolating the salt thus formed. Representative salts include the hydrobromide, hydrochloride, sulfate, bisulfate, nitrate, acetate, oxalate, valerate, oleate, palmitate, stearate, laurate, borate, benzoate, lactate, phosphate, tosylate, citrate, maleate, fumarate, succinate, tartrate, naphthylate mesylate, glucoheptonate, lactiobionate and laurylsulphonate salts, and the like. These may include cations based on the alkali and alkaline earth metals, such as sodium, lithium, potassium, calcium, magnesium, and the like, as well as nontoxic ammonium, quaternary ammonium, and amine cations, including, but not limited to, ammonium, tetramethylammonium, tetraethylammonium, methylamine, dimethylamine, trimethylamine, ethylamine, triethylamine, and the like. See, for example, Berge S. M., et al., xe2x80x9cPharmaceutical Salts,xe2x80x9d J. Pharm. Sci., 1977;66:1-19, which is incorporated herein by reference.
Those skilled in the art are easily able to identify patients having a stroke or at risk of having a stroke, cerebral ischemia, head trauma, or epilepsy. For example, patients who are at risk of having a stroke include, but are not limited to, patients having hypertension or undergoing major surgery.
The invention will be described in greater detail in conjunction with the following specific examples. These examples are provided for illustrative purposes only and are not intended, nor should they be construed, as limiting the invention in any manner. Those skilled in the art will appreciate that modifications and variations of the following examples can be made without exceeding the spirit or scope of the present invention and claims.